Whole-house ventilation strategies boost indoor air quality

 Whole-house ventilation strategies boost indoor air quality

Unfortunately, most people spend about 90 percent of their time indoors exposed to those potential sources of pollution than can lead to discomfort and illness.

That's why ventilation is critical to a healthy environment. People with asthma, allergies and other sensitivities breather easier with clean air. Adequate ventilation can improve indoor air quality by removing airborne irritants, pollutants and lowering the likelihood of mold and mildew.

Whole house ventilation solutions

If you're building a new high-performance home or updating an existing home, you will likely encounter the need for whole-house ventilation. Homes built to tighter standards require balanced ventilation systems. That means intake of fresh air as well as exhausting of stale air. You want to build tight and then ventilate right.

Depending on the HVAC design and the climate where the house is located, a building professional may also include a heat recovery ventilator (HRV) or an energy recovery ventilator (ERV).

For colder climates, the HRV keeps the home supplied with a steady flow of fresh outdoor air. As stale, warm air is expelled, the heat recovery core warms the incoming fresh, colder air before it is distributed throughout the home. This function provides a constant supply of fresh air and helps control humidity.

The ERV is the right choice for warmer climates where it’s necessary to remove humidity from the incoming fresh air as well as exchange heat from the airflow. The ERV transfers moisture from the incoming humid air to the stale air being vented outside. The ERV also tempers the air like the HRV, reducing demand on the heating and cooling system. ERVs are typically ducted as well, and sized based on the square footage of the home.

Zehnder America, maker of HRV/ERV solutions, offers insights into how whole-house ventilation makes a home perform better.

What are some of the advantages of a HRV/ERV system over an exhaust-only system in an energy-efficient home?

You have significant energy savings because with an HRV or ERV, you recover the energy in the room-temperature air.  With an exhaust-only system or relying on natural ventilation, if it’s thirty degrees outside, you’re bringing in thirty-degree air to make up for what you’re exhausting out. You have to reheat that thirty-degree air up to the indoor room temperature, up to sixty-eight degrees or more.

 With an HRV/ERV system in that same scenario you’d be bringing that fresh air back in somewhere around sixty-five or sixty-six degrees so now you’re only having to reheat that air two or three degrees and that’s an awfully big energy savings. It’s also a big comfort savings because your home is not going to be drafty. Through the HRV/ERV the air is coming in to the home at near room temperature.

How does the HRV/ERV contribute to a home's indoor air quality?

If you're going to build a home with a tight building envelope with minimal infiltration and exfiltration, you need a ventilation strategy or the indoor air quality will suffer. With a commonly used exhaust-only system using bath fans for the most part, air is just being pulled out of the house. Most bath exhaust fans are in the 50 cubic-feet-per-minute range. What that means is to make up for that air exhausting the home, 50 cfm of outside air is coming in from somewhere.

With that air coming in, often the best-case scenario is that it’s coming in around your doors or windows. This means you’re still bringing in any pollutants from outside, including allergens as well as heat and humidity or cold temperatures. More than likely the incoming outside air is coming down walls, from attic crawl spaces and other undesirable places. With a balanced HRV system like those from Zehnder, you are able to control the fresh air coming in and filter it before it goes into the living spaces.

With a balanced and dedicated fresh air system, we know that we are bringing in an equal amount of air where it’ll be filtered before it comes into the house. It will also be heated or cooled to more closely match the indoor temperature, making the room feel more comfortable and lowering heating and cooling demand.

The other part is we’re putting it where it needs to be, such as in the bedrooms and other living spaces. With an exhaust-only type of system or a HRV system that’s coupled with the HVAC system, you don’t know where that fresh air is being put and if it’s put in areas the inhabitants will mostly spend time.

Should the HRV system be separate from the HVAC system?

Yes, it should. The two biggest reasons are efficiency and an HRV is most effective when it’s properly balanced. When the fresh air delivered through the HVAC system, you don't control where it goes. With a separate system, you can put the fresh air exactly where you want it like a bedroom or living room.

When the HRV is ducted in the HVAC system, it changes the static air pressure that the HRV experiences in the system. The HRV operates at a much lower pressure than a standard forced air furnace fan. So the HRV has to work much harder to move air against the higher pressure. That dramatically reduces the efficiency of the unit, so the homeowner pays more for utilities and doesn't receive the full benefit of the fresh air circulation through the home.

What makes Zehnder’s HRV system so quiet?

Not only are the units properly designed for maximum quietness but it’s also part of the proper design parameter. The proper design of the system and proper system selection is critical in maintaining quiet operation. Zehnder designs all systems for the correct air distribution components for maximum quietness. We've found that if fans are too loud, people will turn them off and they lose the benefits of the fresh air system.

 

Keeping Humidity Levels in Check

As temperatures cool and we increase the amount of time spent indoors, it’s important to keep indoor air pollutants and allergens at bay. And while most homeowners recognize the importance of regular cleaning to minimize dust and dander buildup, they often overlook less overt warning signs of poor indoor air quality.

Homeowners are especially misinformed about moisture; many don’t associate foggy bathroom mirrors or peeling wallpaper with unhealthy indoor air. We recently issued a national survey and uncovered that less than half of homeowners know the lack of a bathroom fan has a negative impact on IAQ. Even fewer are using those appliances properly.

Bathrooms and kitchens are exposed to a lot of moisture. Excess humidity and moisture can cause mold and mildew growth. These fungi release airborne spores that act like dust in airways, triggering allergies and asthma. Additionally, mold and mildew can create serious damage to your bathroom.

To prevent mold and mildew growth inside the home, especially in bathrooms, basements and laundry areas, those areas must be properly ventilated. If you don't have a bath fan or you're replacing a nonworking one, consider the Broan® Ultra Green Ventilation Fan. It offers high-performing moisture removal that exhausts up to 110 cubic feet of air per minute. It also has the quietest sound rating attainable and an energy efficiency rating almost 10 times greater than Energy Star requires. Model options include humidity and motion-sensing features, and they are extremely easy to install.

Broan-Nutone offers these tips managing home humidity levels:

  • Run a bath fan right before showering and keep it on at least 10 minutes afterward.
  • Test how effective your existing fan is by holding a piece of tissue paper near it. If the fan is removing air properly, the paper will be drawn against the grill and remain there as long as the fan is on. If not, it’s time for a replacement.
  • Wipe down countertops and grout after each bathroom use. It’s an easy way to make sure moisture doesn’t accumulate.
  • Bathroom vents should lead directly outside and never be vented into the attic, where moisture can cause serious problems.

Read more about indoor air quality.


Topics: Energy Recovery & Heat Recovery

Companies: Zehnder America


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